The structural, electronic, magnetic, elastic, thermodynamic, optical, and thermoelectric properties of Heusler alloy were studied in the XA and ordered phases within the framework of density functional theory. The calculated total energies reveal that the ordered phase is the most stable configuration in the ferromagnetic state under the GGA + U approximation. The total magnetic moments of in both the XA and structures are consistent with the Slater-Pauling relation . Analysis of the density of states and band structure reveals that the phase of the compound exhibits metallic nature in spin-up and spin-down orientations, whereas the XA phase is half-metallic. The results of the elastic-property analysis indicate that both studied phases exhibit elastic anisotropy and satisfy Born's mechanical stability criteria. Furthermore, the thermodynamic properties were evaluated using the quasi-harmonic Debye model implemented in the Gibbs code. The optical properties were investigated in detail through a systematic calculation of the relevant optical parameters. Regarding the thermoelectric behavior of the two phases, the transport coefficients were analyzed over the temperature range of 50-800 K.
A dual-function surface plasmon resonance-photonic crystal fiber (SPR-PCF) with a double-sided polished structure is proposed and numerically investigated. This PCF exhibits excellent performance in refractive index (RI) sensing and tunable ultrabroadband polarization filtering. For sensing, it demonstrates a high maximum wavelength sensitivity of 19 800 nm/RIU and the resolution of 5.05 & times; 10-6 RIU in the RI range of 1.23-1.385. For filtering, by simply adjusting the thickness of the dielectric layer zinc oxide (ZnO) and the RI of analyte n a, a tunable ultrabroadband filter can be achieved. Notably, for a 100-nm thick ZnO layer and n a of 1.51, the extinction ratio (ER) over a 700-mu m fiber length is 238.43 dB. The operating bandwidth with an ER above 20 dB is 610 nm, corresponding to an effective filtering range from 1.21 to 1.82 mu m. In comparison, for a 10 nm thick ZnO layer and n a of 1.36, the ER reaches 302.10 dB over the same fiber length, with the bandwidth of 660 nm. The filtering range shifts to longer wavelengths, spanning from 1.34 to 2.00 & micro;m. Owing to its simple structure and exceptional dual-function performance, the proposed PCF presents a significant step forward in the integration and multifunctionalization of compact photonic devices.
Transparent conductive oxides are essential in optoelectronics, but scarce high-performance p-type TCOs hinder all-transparent device development. Sn2Nb2O7, due to its hybridization characteristics of Sn-5s and O-2p orbitals at the valence band top, is highly compatible with the chemical modulation of valence band strategy, making it a promising candidate material for p-type TCOs. In this study, first-principles calculations were employed to systematically investigate the defect formation energy, electronic structure, and optical properties of eight intrinsic defects in Sn2Nb2O7, aiming to explore its p-type performance potential and optimize optoelectronic characteristics. The results show that under oxygen-rich conditions, acceptor defects V Sn, V Nb, Oi, and SnNb readily form spontaneously, whereas V O, Sni, Nbi, and NbSn are significantly suppressed. Among these, V Sn is a shallow acceptor defect that efficiently provides hole carriers, whereas V Nb, although a strong acceptor, introduces deep energy levels leading to hole localization. Optical performance analysis demonstrates that the reflectivity and absorption coefficients of V Sn and V Nb defect systems exhibit excellent transparency in the visible light band without introducing additional light absorption, achieving synergistic optimization of p-type conductivity and high visible light transparency. These findings provide critical theoretical support for the application of Sn2Nb2O7 in all-transparent optoelectronic devices.
A series of in situ high-pressure, high-temperature experiments combining Raman spectroscopy and synchrotron-based X-ray diffraction were conducted on graphite-like BC3. Raman spectroscopy reveals a direct phase transition from graphite-like BC3 to a new boron carbide phase at 1500 K under pressures of 19.9, 38.2, and 47.8 GPa. This new boron-carbon phase retains its structural integrity upon decompression to 5.2 GPa and is the only high-pressure boron-carbon phase synthesized via extreme conditions. Comparative analysis of X-ray diffraction and Raman spectroscopic data for this new boron-carbon phase and the theoretically predicted metastable C3B phase indicates that it is best interpreted as a derivative phase inheriting the topological framework of C3B, yet exhibiting pronounced local structural distortions and microstrain.
Carbon nitride (C3N4) exhibits rich polymorphism arising from versatile sp(2) and sp(3) hybridization. Using graph-space based crystal structure prediction, we identify a previously unreported polar C3N4 polymorph with Pna2(1) symmetry, closely related to the experimentally accessible chiral P4(3)2(1)2 phase. Although constructed from the same ribbon-like CN fragments, Pna2(1) adopts a different stacking sequence that lowers the symmetry and generates a polar structure. Enthalpy calculations show that Pna2(1) is energetically competitive with P4(3)2(1)2 and becomes more stable than graphitic Pbca above similar to 4 GPa, indicating a low-energy metastable mixed sp(2)-sp(3) phase. Simulated X-ray diffraction patterns suggest that Pna2(1) may coexist with P4(3)2(1)2 in high-pressure experiments. First-principles calculations confirm its dynamical and mechanical stability, as well as an indirect bandgap of 3.55 eV. The reduced symmetry further induces spontaneous polarity, enhanced piezoelectricity, and anisotropic optical response. Our results demonstrate how subtle stacking variations within a common fragment-based framework can generate low-energy polar semiconductors with distinct functional properties.
